实体框架 - 导航属性不急切/延迟加载

Question

我有以下诱惑：

public class Ticket 
{
    public int Id { get; set; }
    public string RequestBy { get; set; }
    public int PriorityId { get; set; }
    public ApplicationUser Requester { get; set; }
    public Priority Priority { get; set; }
}
public class ApplicationUser
{
    public ApplicationUser()
    {
        Id = Guid.NewGuid().ToString();
    }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}
public class Priority
{
    public int Id { get; set; }
    public string Name { get; set; }
}

当我在控制器中按如下方式创建新票证时：

 public class BaseController : Controller
{
    protected readonly IUnitOfWork UnitOfWork;
    public BaseController(IUnitOfWork unitOfWork)
    {
        UnitOfWork = unitOfWork; 
    }
}
public class TicketController : BaseController
{
    public TicketController(IUnitOfWork unitOfWork) : base(unitOfWork) { }
    [HttpPost]
    public ActionResult CreateTicket(CreateTicketVM viewModel)
    {
         // repopulate dropdowns incase we need to return view
         // viewModel.Priorities is IEnumerable list
         viewModel.Priorities = UnitOfWork.PriorityRepository.GetPriorities();
        //validation code removed for brevity...
        var ticket = new Ticket
        {
           RequestBy = !string.IsNullOrEmpty(viewModel.RequestBy) ? viewModel.RequestBy : User.Identity.GetUserId(),
           PriorityId = viewModel.PriorityId != 0 ? viewModel.PriorityId : (int)PriorityLevel.Medium,
        };
        UnitOfWork.TicketRepository.Add(ticket);
    }
}

现在，当我在调用.Add(ticket)后调试var ticket时，为什么尽管设置了RequestBy值，但它还是加载了相关的导航属性Priority而不是Requester导航属性？如您所见，我还没有针对任一导航属性定义任何virtual关键字？

仅对ApplicationUser类型的所有导航属性发生束缚此操作。即使不使用 virtual 关键字，所有其他导航属性似乎也会加载???

使用流畅的 api，我定义了 FK RequestBy如下：

modelBuilder.Entity<Ticket>()
 .HasRequired(x => x.Requester)
 .WithMany()
 .HasForeignKey(x => x.RequestBy);

下面是用于提供更多上下文的附加代码。

工单存储库：

public class TicketRepository : ITicketRepository
{
    private readonly ApplicationDbContext _context;
    public TicketRepository(ApplicationDbContext context)
    {
        _context = context;
    }
    public void Add(Ticket ticket)
    {
        _context.Ticket.Add(ticket);
    }
}

优先级存储库：

public class PriorityRepository : IPriorityRepository
{
    private readonly ApplicationDbContext _context;
    public PriorityRepository(ApplicationDbContext context)
    {
        _context = context;
    }
    public IEnumerable<Priority> GetPriorities()
    {
        return _context.Priority.ToList();
    }
}

工作单位：

public class UnitOfWork : IUnitOfWork
{
    private readonly ApplicationDbContext _context;
    public ITicketRepository TicketRepository { get; private set; }
    public IPriorityRepository PriorityRepository { get; private set; }
    public UnitOfWork(ApplicationDbContext context)
    {
        _context = context;
        TicketRepository = new TicketRepository(_context);
        PriorityRepository = new PriorityRepository(_context);
    }
    public void Complete()
    {
        _context.SaveChanges();
    }
}

Answer 1

不应加载这两个导航属性。你看到的内容很可能是所谓的导航属性修复功能的结果 - 如果上下文已跟踪实体，EF 会更新引用它的实体的导航属性，即使你没有专门请求也是如此。

您可以通过使用局部变量而不是_context字段轻松验证var _context = new YourDbContext();这一点。或者像这样：

var ticket = new Ticket
{
    RequestBy = !string.IsNullOrEmpty(viewModel.RequestBy) ? viewModel.RequestBy : User.Identity.GetUserId(),
    PriorityId = viewModel.PriorityId != 0 ? viewModel.PriorityId : (int)PriorityLevel.Medium,
};
bool priorityLoaded = _context.Priority.Local.Any(e => e.Id == ticket.PriorityId);
bool userLoaded = _context.ApplicationUser.Local.Any(e => e.Id == ticket.RequestBy);
_context.Ticket.Add(ticket);

根据您的描述，priorityLoaded应该在userLoaded时true - false.